半封闭压缩机电动机故障分析与排除

在中央空调系统中使用的冷水机组，普遍采用半封闭活塞式压缩机，这种压缩机的电动机直接接触制冷剂和冷冻油，并长期在一定的压力和温度下工作，电动机的工作环境比较恶劣。在机组运行维护过程中，如果使用维护不当，往往会引起电动机烧毁，使空调系统无法正常工作。而维修好的冷水机组，其电机往往容易再次烧毁。本文分析认为造成这类压缩机电动机烧毁故障的主要原因是：系统回油不良；电动机三相电流不平衡；制冷系统含水量大；缺制冷剂运转；真空运转；电源电压过低；异物进入压缩机等。要想避免维修过的压缩机电机再次很快就烧毁，必须将产生该故障的原因解决，并且在维修中不能带入新的故障因素。     

喷雾通风冷却塔在循环冷却水系统中的应用

叙述了煤气压缩机的循环冷却水系统里改用喷雾通风冷却，可以收到良好的效果：降温冷却效果好、节能效果显著、操作维护可靠方便。     

钢筋等强度剥肋滚压直螺纹连接技术的应用

介绍了钢筋等强度剥肋滚压直螺纹连接技术的工艺啄理，并就其加工钢筋丝头的机具设备和该工艺特点进行了阐述，通过技术经济分析，指出该技术连接快捷，施工方便，成本低廉，具有广阔的市场前景。     

高转速压缩机基础设计的几个问题

简捷全面地概述了n>3000r/min的高转速透平压缩机基础的设计与计算历程、振动实例,单自由度、多自由度简化计算以及不作动力计算的论据,对基础构造设计提出若干实用性的建议,为读者提供了修订《动规》(GBJ40-79)第六章透平压缩机基础的背景材料.     

高强螺栓联接的施工工艺和质量检查

结合铁路钢护梁以高强度螺栓联接的施工实例，介绍了扭矩法施拧的施工工艺，从施工准备，高强度螺栓连接副的安装拧紧到施拧结束的全过程及质量检查方法，如终拧标记是否有漏，扭矩误差是否在允许范围内。还指出进行质量检查时应注意的若干事项，高强度螺栓在钢结构安装工程中所起的关键作用。     

Sub-micrometer particulate air pollution and cardiovascular mortality in Beijing, China

Background

While the link between particulate matter and cardiovascular mortality is well established, it is not fully investigated and understood which properties of the aerosol might be responsible for the health effects, especially in polluted mega-city areas.

Objectives

Our goal was to explore the association between daily cardiovascular mortality and different particle metrics in the sub-micrometer range in Beijing, China.

Methods

We obtained daily counts of cause-specific cardiovascular deaths in the Beijing urban area for the period March 2004 to August 2005. Concurrently, continuous measurements of particle number size distributions were performed. Particle number concentrations (NC) between 0.003 μm and 0.8 μm were converted to particle mass and surface area concentrations assuming spherical particles. Semi-parametric Poisson regression models adjusting for trend, seasonality, day of the week, and meteorology were used to estimate immediate, delayed and cumulative particle effects. Additionally, effect modification by air mass origin was investigated.

Results

We observed associations between daily cardiovascular mortality and particle NC for a 2-days delay. Moreover, nearly all particle metrics showed 2-days delayed associations with ischemic heart disease mortality. The strongest association was found for particle NC in the size range 0.03-0.1 μm (7.1% increase in daily mortality with a 95%-confidence interval of 2.9%-11.5%, per an increase of 6250 particles/cm³). Results for surface and mass concentrations with a lag of two days indicated effect modification by air mass origin, whereas effects of particle NC were not modified.

Conclusions

Results show an elevated risk of cardiovascular mortality in Beijing from short-term exposure to particulate air pollution in the sub-micrometer range. Results also indicate that locally produced smaller particles and regionally transported particles may exhibit different effects in Beijing.     

盘壁喷管的三维流场计算和结构设计优选

文中运用UG软件对涡喷发动机火药起动器盘壁式喷管进行整体三维建模,采用FLUENT对起动器喷管进行流场计算,得出在不同设计值下喷管的出口速度。根据分析结果对盘壁喷管结构进行优化设计。     

机电作动器动力学建模与电流跳变现象分析

针对机电作动器在带载位置跟踪性能检测试验中响应曲线峰值点处出现的电流跳变现象,推导机电作动器空气舵负载、永磁同步电机和传动机构的动力学与运动学方程,建立其多非线性因素动力学模型。从电能、动能、摩擦损耗和弹性能间相互转换的角度,解释电流跳变现象,证明电流跳变现象是由传动机构摩擦力瞬间反向造成的。仿真与试验结果表明,在57 N·m^570 N·m负载力矩条件下,电流曲线拟合误差最大为13.06%,决定系数最小为0.87,所建模型提高了机电作动器仿真分析精度,复现了电流跳变现象,对机电作动器功率损耗分析及故障诊断的仿真预估具有重要意义。     

一种驱动螺旋钻机的专用高压变频器

针对开采薄煤层、延长矿井的使用寿命、提高煤炭资源利用率,螺旋钻进式采煤机提供了良好、有效的选择。为螺旋钻机系统设计了防护等级为IP56的1600 kW/3.3 kV变频器。该变频器采用18脉波移相整流的移相变压器,实现电网侧无谐波干扰。拓扑结构上采用多电平功率单元串联技术,输出13电平,正弦度高,d u/d t小,不会损伤电缆和电机绝缘。变频器移相变压器和功率单元均采用水冷散热方式,实现高效、可靠的散热。变频器性能上满足螺旋钻进式采煤机的3倍起动转矩、急加速、急减速等特殊工况要求,并预留远程通信接口,方便用户进行信号控制与数据采集。     

Investigation into the Interaction of Centrifugal Compressor Impeller and Vaneless Diffuser

Theinteractionofcentrifugalcompressorim pelleranddiffusertakesgreateffectontheperfor manceofcentrifugalcompressor.Researchresults showthatwhentheairflowoutoftheimpellerflows throughthediffuser,theefficiencyofthecompressor maydecreaseby10%orso.Soitcanbeofg…